NewCipher
c, err := rc4.NewCipher(key)
if err != nil { log.Fatal(err) }
out := make([]byte, len(in))
c.XORKeyStream(out, in)
// Do NOT use for anything new. Use AES-GCM or ChaCha20-Poly1305.crypto/rc4
RC4 stream cipher. BROKEN. Only for reading legacy protocol data you cannot avoid.